Hypertension is a major cause of morbidity and mortality in persons 60 years of age and older; thus, it may well represent the most serious health problem facing older Americans today. The number of older Americans with hypertension is alarming, with prevalence rates estimated at 25-50%. For the large percentage of these persons with mild hypertension, non-pharmacological interventions such as regular exercise may be preferable to drug therapy if they can be shown to be just as efficacious in lowering blood pressure. Experimental evidence suggests that regular exercise may have a significant blood pressure lowering effect in hypertensive subjects under 50 years of age; however, little information exists on older subjects, on the optimal type of exercise, or on the mechanisms by which reductions in blood pressure are mediated. Therefore, the purpose of the present study will be to determine: (a) if regularly performed, endurance exercise significantly lowers blood pressure in men and women between 60-75 years of age with mild hypertension (blood pressure = 140-170 and/or 90-100); (b) if blood pressure can be reduced with exercise of mild intensity or if more strenuous exercise is necessary; and (c) the mechanisms which mediate training-induced reductions in blood pressure in older hypertensive subjects. To answer these questions, 66 older hypertensive subjects will perform mild (N=23) or strenuous exercise (N=23) or serve as non-existing controls (N=20) for one year or longer. Blood pressure at rest and over the course of an entire day (24-hr. ambulatory recordings) will be determined before and at 6-month intervals during training. Cardiac output, systemic vascular resistance, heart rate, stroke volume, cardiac autonomic efferent activity, cardiac dimensions and contractility, efferent sympathetic nerve activity (SNA), and carotid and cardiopulmonary baroreceptor regulation of heart rate and efferent SNA will be either measured or calculated at the same time points to determine the mechanisms by which blood pressure is reduced. The hypothesis is that regular exercise will reduce blood pressure primarily through a reduction in vascular resistance mediated by a decrease in efferent SNA; the decrease in efferent SNA may be mediated by enhanced baroreceptor efferent inhibitory tone. This proposal is a logical extension of the applicant's previous work and is consistent with his long-term goal of studying the beneficial effects of regular exercise on aging and its associated disorders, and the mechanisms by which these effects are mediated.